D i s t o r t i o n

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Equilibrium has a thread on tool carts. Some responses have been more tables than carts, others are carts, but built for smooth floors. My lifelong wish item has been a three tray cart 30" wide for doorways, 48" long for capacity Each tray would be 3" tall. To roll over rough terrain or cluttered floors strewn with cords or debris it would have 26" tall wheels built for pony sulkies. To keep it light enough to load in the van, it would be built of aluminum .065 thick with bar stock to hold it all together, and form a handle. The bottom tray at 14" above the axle, would have compartments around holes in the floor to put the wheels. The second tray at 27 inches would be above the wheels, the third tray at perhaps 39".Previous projects with 16 gauge aluminum had minimum distortion despite long welds. These trays are a mess! The bottom tray was so distorted I added ribs lengthwise of 1/4" x 2" to pull it flat, The other two weren't bad until I added 1/4 x 2-1/2 x 12" reinforcing plates to the flat bottom. Now, laying the should be flat tray on a flat surface, one corner is 5" up! I'm getting frustrated! What did I do wrong? Can it be salvaged? Should I do it over again I'd use a frame, with only small welds holding sheet metal on it. The tray sides are bent in a brake but the ends are pieces welded in. I want to build a press brake to bend up 4 sides requiring only 4 3" outside corner joints to weld on each tray.
Reply:Your trays are 30 inches by 48 inches?  You can always bend three edges on shallow tray before you have problems on a brake.  Form one of the side edges then the back at one end of the machine and then the other end at the other end of your machine.  If you used a gooseneck die and gave yourself a top edge turned in 90 degrees that would stiffen things even more.  For the third side of your tray form up a strip into a U shape with two small legs.  Fit it to the end and the extra flanged material will prevent distortion.  Stitching it would be better and since you have formed the edges it is realistic to do.  That takes care of the edges but you have a wide expanse in the middle of the tray that will oil can.  Maybe form up two pieces 30 by 24 to make a single tray when tacked together.
Reply:Maybe you could have cut the end pieces  3 & 3/4" wide and bent the 3/4 to go under the trays. It would help to stiffen the tray and you would only need a few short welds across the bottom to hold it in place. Or a finger brake and just cut 3" squares out of each corner and bend them up.---Meltedmetal
Reply:I think fabrication of trays was manageable. I had some distortion, but could live with it. It's when I welded a couple of pads to receive the vertical riser from the axle to the middle tray all went impossibly bad. I tacked, then step welded, leaving plenty of time to cool. Distortion went out of control.
Reply:Threaten it with a big hammer. Better still two.---Meltedmetal